Mitrovic was told to work harder in training, with his efforts tracked by a GPS vest.
However, the Serbian was reportedly not performing better than the likes of Dwight Gayle, Joselu and Ayoze Perez.
Benitez even asked Newcastle’s backroom staff whether he should be giving Mitrovic a chance, but they were all of the same opinion that the target-man needed to improve in training.
Mitrovic was ultimately loaned out to Fulham in January, and his form in the Championship has caused some frustration with supporters of the Tynesiders.
While Newcastle have continued to struggle to find a prolific scorer, Mitrovic has found the back of the net frequently for Fulham.
The powerful forward now has five goals in his last four appearances for Slavisa Jokanovic’s side, and is spearheading their push for promotion.
Newcastle did sign Islam Slimani on loan to replace Mitrovic, but the Algerian striker is still out with injury.